A conventional technique will be described with reference to FIG. 4 by taking a case of exposing a pattern 20 shown in FIG. 2 as an example.
In a variable shaping method standing for the conventional technique, the shape of a charged beam is of only rectangle and therefore, as shown in FIG. 4, exposure has to be carried out by making a division in compliance with a pattern form. Accordingly, for a pattern having a number of inclined lines and a pattern having complexity, the number of shots is correspondingly increased and as a result the throughput is decreased. Especially, the number of exposure shots increases drastically for exposure of a highly integrated electronic memory device or the like having a large number of patterns and hence it takes a long time for exposure.
The aforementioned conventional technique fails to fully take into consideration a high speed processing of exposure of the highly integrated electronic memory device and the like having periodical repetition and a large number of patterns. To solve this problem, an exposure method shown in JP-A-59-169131 is available. According to this idea, the charged beam shapes are prepared including, in addition to the rectangle, shapes forming one element portion of pattern such as a pattern 23 and a pattern 24 which are shown in FIG. 3. However, the conventional aperture material is a metallic material having bad workability and practically speaking, the aperture can not be formed with a complicated shape, for example, comparable to a 64-mega bit dynamic random access memory (hereinafter abbreviated as Mb DRAM). Further, in the above example, only portions of a pattern such as a single inclined line or single polygonal line are exposed collectively but the form inclusive of even an array of pattern is not taken into account. Therefore, making a pattern division is still required and a drastic decrease in shot number can not be achieved. In addition, when shot density per unit area is increased concomitantly with high integration, the total shot number is correspondingly increased.